1. Field of the Invention
The present invention relates to a bicycle transmission mechanism, more particularly to a free-wheel hub transmission mechanism for a bicycle.
2.Description of the Related Art
Referring to FIG. 1, a conventional free-wheel hub transmission mechanism is shown to include an axle 3, a spoke-mounting barrel 1 rotatably mounted around the axle 3 in such a manner that a right axle portion 300 thereof projects outwardly from a right end portion 100 of the spoke-mounting barrel 1. A sprocket mounting member 2 is sleeved around the right axle portion 300 of the axle 3 adjacent to the right end portion 100 of the spoke-mounting barrel 1. The sprocket-mounting member 2 includes an outer shell 201, upon which a sprocket (not shown) is adapted to be mounted, and an inner shell 203 disposed rotatably within the outer shell 201 around the right axle portion 300 by means of a ratchet mechanism. The inner shell 203 has a barrel-coupling portion 206, which extends into and which engages threadedly an internally threaded right end portion of the spoke-mounting barrel 1 such that the spoke-mounting barrel 1 is co-rotatable with the inner shell 203 of the sprocket-mounting member 2 in a single direction.
Some of the drawbacks of the aforementioned conventional free-wheel hub transmission mechanism are as follows:
The inner shell 203 of the sprocket-mounting member 2 has a central hole of a polygonal cross section adapted to receive an operating tool for rotation of the same with respect to the spoke-mounting barrel 1 prior to insertion of the axle 3 through the sprocket-mounting member 2 and the spoke-mounting barrel 1. It is noted that during assembly of the conventional hub transmission mechanism, a relatively large torque, as high as 2000 kgf-cm, is required to tighten the barrel-coupling portion 206 of the inner shell 203 in the internally threaded right end portion of the spoke-mounting barrel 1.